The present invention relates to a dryer for compressed gas and to a compressor installation and a method for drying gas.
Dryers for compressed gas are already known, which dryers are provided with a vessel containing a drying zone and a regeneration zone, and possibly a cooling zone; a first inlet to the drying zone for the supply of the compressed gas to be dried and a first outlet from the drying zone for the removal of dried gas; a second inlet to the regeneration zone for the supply of a warm regeneration gas and a second outlet from the regeneration zone and the optional cooling zone; a rotatable drum in the vessel with a regenerable drying agent therein and drive means for rotating said drum such that the drying agent is moved successively through the drying zone and the regeneration zone, whereby said second outlet of the regeneration zone and the optional cooling zone is connected to said first inlet of the drying zone by means of a connecting pipe with a cooler and condensate separator therein, and whereby said dryers are configured such that, during the operation of the dryer, the gas flow rate leaving the regeneration zone and the possible cooling zone via the second outlet is equal or almost equal to the gas flow rate that is subsequently guided via the first inlet into the drying zone to be dried.
An example of a dryer in which the regeneration gas flow rate leaving the regeneration zone corresponds to the flow rate of gas to be dried that is guided into the drying zone is described in WO 01/87463. The warm compressed gas is first guided through the regeneration zone where it acts as a regeneration gas and absorbs moisture from the drying agent for the regeneration of this drying agent. In the embodiment described in WO 01/87463, ambient air is compressed for example, for example by means of an air compressor, and this air not only undergoes a pressure increase during compression but also experiences a temperature increase, such that the relative humidity of this air falls and this air is able to absorb moisture from the drying agent. Dryers that make use of the heat of compression present in the compressed regeneration gas are also known in industry by the name ‘heat of compression’ dryers or HOC dryers.
After passing through the regeneration zone the warm regeneration gas presents a higher relative humidity. The moist gas leaving the regeneration zone is then guided through a cooler in the connecting pipe such that the temperature of this gas falls to below the pressure dew point and condensation of the moisture in the gas occurs. The droplets thereby formed are then removed by means of the condensate separator such that the now cooled compressed gas is 100% saturated and is guided in its entirety to the first inlet of the drying zone and then through this drying zone, where the drying agent extracts moisture from this compressed gas by means of sorption (adsorption and/or absorption). The dried gas leaving the drying zone can be used in a compressed air network located downstream of the dryer for all kinds of purposes, such as pneumatic transport, driving pneumatically powered tools, and similar.
It is characteristic of the type of dryer described above in WO 01/87463 that the full or practically full flow of compressed gas originating from the compressor is first guided through the regeneration zone, and then fully through the drying zone. Dryers that make use of such a full flow of the gas through the regeneration zone and the drying zone are also called full-flow dryers.
In other arrangements, for example as described in WO 2006/012711, the bulk of the warm compressed gas leaving the compressor is first guided through an ‘aftercooler’ to then be guided to the drying zone. Only a portion of the warm compressed gas is tapped off downstream from the compressor and upstream from the aftercooler in order to be guided to the regeneration zone for regeneration of the drying agent. Such a dryer as described in WO 2006/012711 is thus a heat-of-compression dryer, but does not operate according to the full-flow principle, as it is not the entire flow of warm compressed gas that is used as a regeneration gas.
WO 2011/017782 also describes a heat-of-compression dryer that does not operate according to the aforementioned full-flow principle. The dryer as described in WO 2011/017782 presents the particular characteristic that the regeneration zone comprises two subzones, i.e. a first subzone through which a first regeneration flow is guided and a second subzone through which a second regeneration flow is guided, and whereby the dryer is configured such that the relative humidity of the aforementioned second regeneration flow is lower than the relative humidity of the aforementioned first regeneration flow that is guided through the first subzone. The second subzone is preferably at the end of the regeneration zone. In this way more moisture can be absorbed from the drying agent than in a conventional way, such that more moisture can then be sorbed by the drying agent from the gas to be dried in the drying zone.
With such a dryer according to WO 2011/017782 it may be that in certain circumstances, for example when starting a compressor that supplies a gas to be dried to the dryer, the desired flow of the second regeneration flow cannot be realised as the pressure in the drying zone has not built up sufficiently. In some cases gas from the regeneration zone can even temporarily enter the outlet of the drying zone through any leaks or even the tap-off pipe, which could result in undesired dew point peaks. The aim of the present invention is to avoid this in as many possible circumstances.